Search for a kaonic nuclear state via $^4$He$(K^-, N)$

TL;DR

This study reanalyzed data from experiments searching for a kaonic nuclear state, finding no narrow peak previously reported, and suggests the earlier signal was likely an artifact, though wider structures cannot be ruled out.

Contribution

The paper provides a detailed reanalysis of experimental data, challenging previous claims of a narrow kaonic nuclear state and improving understanding of the reaction mechanisms involved.

Findings

No narrow ($ extasciitilde$20 MeV) peak observed in the new data

Previous peak attributed to experimental artifact

Wider structures remain possible and are under investigation

Abstract

Very recently, we have performed a couple of experiments, {\it{KEK PS-E549/E570}}, for the detailed study of the strange tribaryon $S^0(3115)$ obtained in {\it{KEK PS-E471}}. These experiments were performed to accumulate much higher statistics with improved experimental apparatusespecially for the better proton spectroscopy of the $^4$He({\it{stopped K}}$^-$, {\it{N}}) reaction. In contrast to the previous proton spectrum, no narrow ($\sim$ 20 MeV) peak structure was found either in the inclusive $^4$He({\it{stopped K}}$^-$, {\it{p}}) or in the semi-inclusive $^4$He({\it{stopped K}}$^-$, {\it{p}}$X^\pm$) reaction channel, which is equivalent to the previous $E471$ event trigger condition. Detailed analysis of the present data and simulation shows that the peak, corresponding to $S^0(3115)$, has been an experimental artifact. Present analysis does not exclude the possible existence of a much wider structure. To be sensitive to such structure and for better understanding of the non-mesonic $K^-$ absorption reaction channel, detailed analysis of the data is in progress.